The present invention relates to methods and apparatuses for enabling a pin on an IC package to serve a dual function. More particularly, the present invention relates to method and apparatuses for enabling an IC pin to serve both an input and a timer function without the addition of a control pin by taking advantage of capabilities inherent in the pins serving the timer function.
In the manufacturing of modern integrated circuits (IC), it is highly desirable to integrate multiple functions into one IC package in order to offer customers more functions in increasingly smaller packages. The ability to integrate multiple functions into one IC package gives customers access to more functions with fewer IC's. Consequently, a given circuit design task may be accomplished with fewer IC's, thereby saving design effort and costs.
From a manufacturer's perspective, the ability to provide multiple functions in an IC offers significant competitive advantages. By offering more functions within a chip, a manufacturer may be able to differentiate their products in the competitive market place. The ability to provide multiple functions also offers significant cost saving advantages. Even if a customer is unable to make use of all the offered functions in an IC chip, the fact that multiple functions are integrated into one IC permits the manufacturer to configure the same manufactured IC part to perform different functions to meet the needs of different customers. In this manner, the number of different IC chips that must be manufactured and kept in inventory may be reduced since the same manufactured IC chip can, in effect, be configured to appear as different parts to different customers.
In the prior art, increasing a chip's functionality typically requires additional pins, e.g. input, output, and control pins. However, as pins are added to an IC chip to offer additional functions, the size of the IC chip grows correspondingly. Since it is also desirable to keep the physical size of the IC packages as small as possible, chip designers are confronted with a dilemma. On the one hand, as IC packages become smaller and smaller, the number of pins that can be physically attached to the miniaturized package diminishes, thereby limiting the number of functions that can be offered using the prior art method. On the other hand, IC chips need to be endowed with an increasingly sophisticated set of functions to remain competitive. To provide for an ever increasing number of functions offered in each IC package, designers constantly search for ways to more efficiently utilize the limited number of pins in modern pin-limited IC packages.
By way of example, in a class of applications known as voltage regulation circuits, there is often required a timer circuit for sequencing different subcircuits of the voltage regulator IC. For example, a timer may exist in a typical voltage regulator for activating a first subcircuit, say a 5 volt power supply for some period of time before activating a second subcircuit, say a 3.3 volt power supply. The presence of a timer function such as the above-described typically requires at least 3 pins: a sequencing pin to dictate the sequence of subcircuit activation, i.e. which subcircuit should be activated first in time and which subcircuit should be activated later, a start pin to provide the signal for starting the sequence, and a timer pin for adjusting the time delay between the activation of the first subcircuit and the subsequent activation of the second subcircuit.
The use of three dedicated pins to provide a timer function in an IC circuit reduces the number of available pins that can be used for other functions. In the prior art, the pins that serve the timer function are dedicated, i.e. they can not be employed in other capacities to provide additional functionality in the IC circuit. The inability to use the pins that are dedicated to the timer function for other purposes reduces the set of functions that can otherwise be offered by the pin-limited IC circuit. If there is a way to enable an IC pin to serve both an input and a timer function, the IC can be endowed with additional functions without requiring the addition of pins and the concomitant increase in package size.
What is needed is a method and apparatus for utilizing the pins that are dedicated to the timer function to serve another function. Such improved apparatus and method would advantageously allow one or more of these dedicated pins to serve multi-functions, thereby increasing the number of functions that can be offered by modern pin-limited IC circuits.